1. Technical Field of the Invention
The present invention is directed to high-quality electrophotography, using small toner particles, and using at least two different types of exposures or transfer methods, depending on the surface properties of the receiver used.
2. Description of the Prior Art
Toner particle size plays a key role in determining image quality in electrophotography, smaller particles generally yielding better image quality. However, as the particles get smaller, the physics of the forces holding the particles to the photoconductor changes drastically, needing new methods to effectively transfer them from the photoconductor to the receiver.
One such new method is thermally assisted transfer, disclosed in U.S. Pat. No. 4,927,727, issued to Rimai et al. U.S. Pat. Nos. 4,994,827; 5,151,717; and 5,047,791, all issued to Jamzadeh et at, disclose color printers that, by using small toner particles and thermally assisted transfer, produce pictorial quality images on thermoplastic-coated receivers. It is apparent from these disclosures that a thermoplastic-coated receiver is necessary for thermally assisted transfer. It should be noted that with the use of thermoplastic-coated receivers, the extra cost of coating a thermoplastic layer on plain paper could be a deterrent in some applications. Another disadvantage of using thermoplastic-coated paper is the nonrecyclability. A further problem with thermoplastic-coated paper is the extra difficulty of handling them because they are easily charged up electrostatically. Also, there are certain applications where the surface of the receiver must be non-smooth and somewhat rough, e.g., greeting cards.
U.S. Pat. Nos. 4,181,423 and 4,006,983, issued to Pressman et at, disclose an electrostatic color printer that is capable of printing on coated and uncoated paper. However, this printer is not able to handle the electrostatic transfer of small toners because of complications, such as those explained in U.S. Pat. No. 4,927,727. Furthermore, the exposure step in the disclosed patents has not been modified according to the type of receiver used. It can be seen that changing the exposure method depending on the surface smoothness of the receiver will improve the image quality considerably.
U.S. Pat. No. 5,282,001, issued to Watson, teaches of "selectively variable operating parameters in accordance with differing characteristics of sheets to be used". Specifically, it teaches of changing "the time starting to form a buckle in each of the sheets just prior to transfer of a developed image" according to the type of the sheets used. The single property of the sheet that is identified as the distinguishing factor is the weight of the receiver, i.e., normal 80 g. m.sup.-2 versus heavy card stock. This patent does not refer to the surface smoothness of the receiver as a distinguishing factor for process modifications. Consequently, it does not teach of the difficulties of transferring small toner particles to paper having different surface characteristics. Furthermore, it does not teach the use of different techniques of electronic exposure to accommodate different transfer requirements. The disclosure teaches of "setting operating parameter values from a non-volatile memory", i.e., selecting different but fixed parameters but it does not teach of using different methods.